1. Field of Invention
The invention is directed to fracturing tools for use in oil and gas wells, and in particular, to fracturing tools having multiple crossover sub-assemblies or subs capable of being selected during multi-zone fracturing processes.
2. Description of Art
Fracturing or “frac” systems or tools are used in oil and gas wells for completing and increasing the production rate from the well. In deviated well bores, particularly those having longer lengths, fracturing fluids can be expected to be introduced into the linear, or horizontal, end portion of the well to frac the production zone to open up production fissures and pores therethrough. For example, hydraulic fracturing is a method of using pump rate and hydraulic pressure created by fracturing fluids to fracture or crack a subterranean formation.
In addition to cracking the formation, high permeability proppant, as compared to the permeability of the formation can be pumped into the fracture to prop open the cracks caused by a first hydraulic fracturing step. For purposes of this disclosure, the proppant is included in the definition of “fracturing fluids” and as part of well fracturing operations. When the applied pump rates and pressures are reduced or removed from the formation, the crack or fracture cannot close or heal completely because the high permeability proppant keeps the crack open. The propped crack or fracture provides a high permeability path connecting the producing wellbore to a larger formation area to enhance the production of hydrocarbons.
To facilitate fracturing of the well and returning wellbore fluids, including produced hydrocarbons, back to the surface of the well, some fracturing tools include a crossover sub-assembly or sub having two pathways. Proppant is pumped downhole through one pathway and into the formation and producing fluids are returned back uphole to the surface of the well through the other pathway. In multi-zone fracturing processes, the crossover sub is used repeatedly in each zone which can decrease the life of the crossover sub requiring repairs or replacements before the fracturing process is completed across each of the multi-zones.